The broad long-term objective of this research is to elucidate the function of the volatile pheromone-detecting neurons expressing orphan odorant receptors. Volatile pheromones trigger or modulate social behaviors including mating. This work is significant because understanding pheromone biology in Drosophila will translate into new methods to control reproduction in insects that transmit human diseases and destroy crops and will shed new insights into the circuits guiding social behavior in an animal model system. Using a multifaceted approach that includes genetics, chemistry, electrophysiology, behavior and imaging we will identify ligands for these receptors, determine the behavioral effects of inactivating and activating these individual neural circuits, and map the downstream circuits activated by these neurons. The first aim is to determine the behaviors influenced through neurons expressing Or83c, which we have identified as a receptor for farnesol. The second aim is to identify ligands that trigger changes in activity in ten orphan trichoid receptors using the 'empty trichoid neuron' system, localize the endogenous neurons expressing these receptors, and characterize their downstream signal transduction requirements. The third aim is to identify behaviors modulated by activation or inactivation of these circuits triggered by odorant stimulation of these receptors. Aim 4 is to map the synaptic targets of the second order projection neurons innervating the trichoid glomeruli using the MARCM approach to begin to trace the neuroanatomy of these behavioral circuits. The completion of the studies will advance our understanding of volatile pheromone biology in an important model system, will identify new targets to manipulate insect behavior, and will guide future studies on pheromone signaling in more complex animal model systems. PUBLIC HEALTH RELEVANCE: Pheromones mediate social behaviors in insects. Insects carry human diseases that kill millions of people every year; malaria alone accounts for over one million deaths annually. Many insect behaviors, including mating, are triggered by pheromones, therefore understanding pheromone biology will provide new targets to manipulate pheromone signals, with the long-term goal of blocking mating in pathogenic insects. We propose to explore the function of orphan pheromone receptors to understand what they do and how they work and what neuronal circuits they activate. The results of these studies will guide future social behavioral experiments in more complex vertebrate animals.